Instabilities in birefringent and periodic optical fibres

Summary form only given. The author reviews certain nonlinear phenomena in optical fibres that rely on the interaction between an intensity-dependent refractive index and a built-in structural modification of the optical fiber. The structural modification might be the presence of a uniform linear birefringence or of a periodic variation of the fiber´s refractive index (i.e. an index grating). In either case, when the light-induced change in the refractive index is large enough to overcome the effects of the linear birefringence or of the index grating, drastic changes in the properties of a transmitted light beam can occur. In the first case, competition between the existing birefringence and the light-induced birefringence leads to an instability in the polarization state of the light beam. This instability has applications to ultrafast all-optical switching devices. In the second case, the combined effects of the index grating and the intensity-dependent refractive index results in optical-bistability, pulse compression, and soliton propagation. The predicted and observed phenomena will be reviewed and discussed within the context of coupled-mode theory